This invention relates to a material handling apparatus, and more particularly to a closed system for handling powdered or fine granular materials, the system enabling the powdered material to be readily unloaded from a container substantially without the discharge or escape of dust. The invention can be used for any application in which it is desired to transfer a bulk supply of a powder into a receiving vessel or into a process of use. A particular useful application that will be described herein is the use of the invention for bulk feeding of powder into a laser sintering process.
In handling powders, such as paint pigments, cement, diatomaceous earth, and chemical powders, both organic and inorganic, it has long been a problem to effect rapid and controlled loading of the material into its container and the rapid unloading of the material without dispensing substantial quantities of dust into the atmosphere. For example, in filling paper bags, drums, or other containers with a powder, substantial quantities of dust are often generated. While this dust can oftentimes be collected or otherwise controlled at the factory in which the bags are filled, the end use of the bags may result in the excessive release of dust that cannot readily be controlled. This release of some types of dust, such as a toxic dust, not only creates a housekeeping problem in the area of use, but the toxic dust may constitute a health hazard to many workers and other personnel in the general vicinity.
As disclosed in U.S. Pat. Nos. 4,182,386 and 5,271,439 containers are now commercially available from Semi-Bulk Systems, Inc. of St. Louis, Mo., for receiving, transporting and unloading “semi-bulk” quantities (e.g., 2000-4000 pounds or more) of powdered or finely divided granular material. Generally, such containers have a rigid molded plastic pallet base and a flexible plastic film bag secured thereto. Methods and apparatus for filling such bags while minimizing generated dust have been described, with one example described in aforementioned U.S. Pat. No. 4,182,386.
A useful system for unloading powdered materials from such flexible containers is described in U.S. Pat. No. 5,271,439. Because many commercial powdered materials may agglomerate and form lumps during transport and storage, the system described in U.S. Pat. No. 5,271,439 employs a joint strategy of vibration and mechanical squeezing of the flexible container while introducing compressed gas into the flexible container to fluidize the powdered material and assist it to flow out of the base of the container. Further, the base of the flexible container is sloped toward one side to help the fluidized powder flow toward the outlet line. In some implementations the entire flexible container may even be tilted to aid flow.
The requirements of vibration, squeezing, and tilting of the flexible container to ensure adequate unloading of the contents lead to a mechanically complex and expensive base and frame for the container and requires that the container must be flexible. Thus there is a need for a much simpler implementation of powder unloading that has less mechanical complexity and is more affordable.
An important application requiring a supply of powder feed is the use of laser sintering technology to produce 3-dimensional articles from powder. By way of background, an example of a freeform fabrication technology is the selective laser sintering process practiced in systems available from 3D Systems, Inc., in which articles are produced from a laser-fusible powder in layerwise fashion. According to this process, a thin layer of powder is dispensed and then fused, melted, or sintered, by laser energy that is directed to those portions of the powder corresponding to a cross-section of the article. Conventional selective laser sintering systems, such as the Vanguard system available from 3D Systems, Inc., position the laser beam by way of an optics system using galvanometer-driven mirrors that deflect the laser beam. The deflection of the laser beam is controlled, in combination with modulation of the laser itself, to direct laser energy to those locations of the fusible powder layer corresponding to the cross-section of the article to be formed in that layer. The computer based control system is programmed with information indicative of the desired boundaries of a plurality of cross-sections of the part to be produced. The laser may be scanned across the powder in raster fashion, with modulation of the laser affected in combination therewith, or the laser may be directed in vector fashion. In some applications, cross-sections of articles are formed in a powder layer by fusing powder along the outline of the cross-section in vector fashion either before or after a raster scan that “fills” the area within the vector-drawn outline. In any case, after the selective fusing of powder in a given layer, an additional layer of powder is then dispensed, and the process repeated, with fused portions of later layers fusing to fused portions of previous layers (as appropriate for the article), until the article is complete.
Detailed description of the laser sintering technology may be found in U.S. Pat. Nos. 4,863,538; 5,132,143; and 4,944,817, all assigned to Board of Regents, The University of Texas System, and in U.S. Pat. No. 4,247,508 to Housholder, all specifically incorporated herein by reference in pertinent part.
Growing use of laser sintering technology, especially in limited run manufacturing and in the use of multiple machines in large service bureaus, has created a need for more automated means for feeding, removing, and recycling of the powders used. Automating powder recycling can significantly reduce manual handling of powders, reduce exposures to the powders, and improve the consistency of the powders being fed to the sintering apparatus. A compact and reliable automated system for feeding to, removing from, and recycling powders within laser sintering systems is described in co-pending patent application Ser. No. 11/077,304, filed Mar. 9, 2005 and assigned to the assignee of the present invention. This application is specifically incorporated by reference herein in pertinent part.
The transfer of new or virgin powder into either the automated powder recycle system described in the aforementioned patent application Ser. No. 11/077,304 or directly into a laser sintering system can take place. What is needed then is a new powder transfer system with a powder container that is portable, but enclosed and therefore dust free, mechanically simple, reliable and lower in cost. These problems are solved in the design of the present invention.